Development of high resolution optical instruments having optical imaging capabilities has necessitated corresponding developments in high resolution imaging lens assemblies. While high resolution optical imaging lens assemblies are known, such assemblies include a large number of lens elements. Additionally, the prior art lens assemblies generally rely on spherical-surface glass lenses as optical elements, including in certain cases, where two spherical glass lenses may be adhered together to form a doublet to correct chromatic aberration. Certain prior art lens assemblies do comprise two-element lens assemblies—however such two—element lens assemblies either have a lower focal ratio (e.g. F/15 for CaF2 with Schott K7) or a lower Strehl Number (CaF2 and BAK2). Yet further, these prior art arrangements result in complicated and/or relatively expensive manufacturing requirements.
There is accordingly a requirement for optical imaging lens assemblies that work in a relatively wide spectral range and that achieve a reduction in the number of lens elements in medium and large aperture systems, while enable manufacturing efficiencies and simultaneously maintaining image quality.
The present invention addresses this need by providing a novel and inventive lens assembly comprising a two-element lens arrangement configured to deliver high level correction of chromatic aberrations and a Strehl Number of more than 80% within the 0.435-0.706 μm spectral range and having focal ratio within F/5-F/12 range—using aspheric surface or surfaces.